Physical properties of High Arctic tropospheric particles during winter

L Bourdages,E W Eloranta,T J Duck,G Lesins,J R Drummond

doi:10.5194/acp-9-6881-2009

L Bourdages, E W Eloranta + Show 3 more

Open Access

https://doi.org/10.5194/acp-9-6881-2009

Copy DOI

Abstract

Abstract. A climatology of particle scattering properties in the wintertime High Arctic troposphere, including vertical distributions and effective radii, is presented. The measurements were obtained using a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: boundary-layer ice crystals, ice clouds, mixed-phase clouds, and aerosols. Two-dimensional histograms of occurrence probabilities against depolarization, radar/lidar colour ratio and height are given. Colour ratios are related to particle minimum dimensions (i.e., widths rather than lengths) using a Mie scattering model. Ice cloud crystals have effective radii spanning 25–220 µm, with larger particles observed at lower altitudes. Topographic blowing snow residuals in the boundary layer have the smallest crystals at 15–70 µm. Mixed-phase clouds have water droplets and ice crystal precipitation in the 5–40 µm and 40–220 µm ranges, respectively. Ice cloud crystals have depolarization decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere (0.5–3.5 km altitude). Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

Highlights

The climate of the Arctic troposphere is known to be sensitive to change (Serreze et al, 2009), but a detailed understanding of infrared radiative transfer central to the problem remains limited by the availability of suitable measurements
An experimental effort to provide comprehensive yearround measurements in the High Arctic has been undertaken by the Canadian Network for the Detection of Atmospheric Change (CANDAC), who established the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut Territory (80◦N, 86◦W) in collaboration with Environment Canada (EC)
A suite of remote-sensing and insitu instruments was installed by CANDAC and the National Oceanic and Atmospheric Association (NOAA) Study of Environmental Arctic Change (SEARCH) programme

Summary

Introduction

The climate of the Arctic troposphere is known to be sensitive to change (Serreze et al, 2009), but a detailed understanding of infrared radiative transfer central to the problem remains limited by the availability of suitable measurements. Experimental progress has historically been impeded by accessibility barriers to the remote North and the harsh environmental conditions. This is true for the High Arctic during winter, when 24 h darkness leads to mean surface temperatures in the vicinity of −40◦C (Lesins et al, 2009b). An experimental effort to provide comprehensive yearround measurements in the High Arctic has been undertaken by the Canadian Network for the Detection of Atmospheric Change (CANDAC), who established the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut Territory (80◦N, 86◦W) in collaboration with Environment Canada (EC). Several different instruments can characterize tropospheric particles, which are known to play a key role in the Arctic radiative exchange (Curry et al, 1993)

Methods

Findings

Discussion

Conclusion